This invention relates to a HOUT position control circuit used to control position where image is displayed in a display.
Multisync monitors use a HOUT position control circuit to control the delay amount from input horizontal synchronous signal (hereinafter referred to as xe2x80x98Hsync signalxe2x80x99) to output horizontal drive signal (hereinafter referred to as xe2x80x98Hout signalxe2x80x99) so as to conduct the control of image display position (hereinafter referred to as xe2x80x98position controlxe2x80x99).
Conventionally, in the HOUT position control circuit of multisync monitors, an adjustable delay circuit is provided in PLL loop, and the position control is conducted by controlling the delay value of the adjustable delay circuit.
FIG. 1 is a block diagram showing the composition of a conventional HOUT position control circuit.
As shown in FIG. 1, the conventional HOUT position control circuit is provided with adjustable delay circuits 24, 25 at the input stage of a phase comparator 3. Two input signals to the phase comparator 3 are separately delayed by the adjustable delay circuits 24, 25. The position control is conducted by controlling the delay value.
FIG. 2 is a block diagram showing the composition of the adjustable delay circuits 24, 25 in FIG. 1.
Multisync monitors need the delay amount to be a same proportion to input Hsync signal. Therefore, sawtooth wave 31 synchronized with input signal 29 of the adjustable delay circuits 24, 25 is generated by a sawtooth generator circuit 28, and then delayed output signal 27 is made by using a comparator 32.
The control of delay value is conducted by using delay control voltage 30, which is DC voltage.
FIG. 3 is a timing chart showing the process of generating a delay value from sawtooth wave.
However, since the conventional HOUT position control circuit has the adjustable delay circuit in PLL loop, a dispersion in the adjustable delay circuit may cause a deviation in position.
Further, since the adjustable delay circuit is operated in analogue manner, the delay value may vary depending on a noise thereby causing a jitter.
Accordingly, it is an object of the invention to provide a HOUT position control circuit that can suppress a deviation in position or a jitter.
It is a further object of the invention to provide a position control circuit used to control the vertical position of display image in a multisync monitor that can suppress a deviation in position or a jitter.
According to the invention, a HOUT position control circuit used to control the horizontal position of display image in a multisync monitor, comprises:
a first PLL circuit that is phase-locked with input horizontal synchronous signal;
a second PLL circuit that is phase-locked with output of the first PLL circuit; and
means for generating a delay between outputs of the first PLL circuit and the second PLL circuit to control the delay amount from the input horizontal synchronous signal to output horizontal drive signal.
According to another aspect of the invention, a HOUT position control circuit used to control the horizontal position of display image in a multisync monitor, comprises:
the position control of display image is conducted in digital manner.
According to another aspect of the invention, a position control circuit used to control the vertical position of display image in a multisync monitor, comprises:
a first PLL circuit that is phase-locked with input vertical synchronous signal;
a second PLL circuit that is phase-locked with output of the first PLL circuit; and
means for generating a delay between outputs of the first PLL circuit and the second PLL circuit to control the delay amount from the input vertical synchronous signal to output vertical drive signal.
According to another aspect of the invention, a position control circuit used to control the vertical position of display image in a multisync monitor, comprises:
the position control of display image is conducted in digital manner
Also, the invention offers a multisync monitor using the above-composed HOUT position control circuit or a position control circuit.